The invention relates to a method for determining the compression factor of powders for processing by means of roller presses having roller diameters of 100 to 400 mm.
Roller presses serve for pressing powders so as to form scabbed strips which are subsequently comminuted into granulate (EP-A-0 525 135). This process is referred to as the dry granulation method. The pressing of the powder takes place between 2 mutually opposed rollers, and, depending on the manufacturer, both rollers are mounted fixedly, that is to say have a fixed roller nip, or one of the two rollers is designed to be movable, is subjected to hydraulic force and has a variable roller nip.
All roller presses have at least 2 press rollers and, depending on the manufacturer, are offered with various roller dimensions. The rollers are fed with powder either by means of gravity or with the assistance of a filling worm.
The dry granulation method enjoys a special status in economic terms in the pharmaceutical industry for the production of granulate, instead of the known wet granulation method.
In the initial phase of development of a new drug, it has been necessary hitherto to dispense with development aimed at dry granulation as the most cost-effective production method, because the powder quantities required for a test are not available or are too costly. Most roller presses also lack appropriate instrumentation for obtaining useful data for the intended development.
A suitable device is known according to EP-A-0 525 135. This device delivers reproducible results even with powder quantities as low as 100 ml.
In the first development phase, only substantially smaller quantities (for example, 10 ml) are available for tests. The subsequent production method must be defined as early as at this stage.
Tablets or capsules can be produced from granulate manufactured by known methods. The most important technological properties, such as the typical entering angle and, resulting from this, the possible compression factor of the powder and also the product quantity per unit time, cannot be ascertained by tabletting.
The object of the invention is to provide a method for testing a powder for its suitability for the production of granulate by the dry granulate method with roller presses on an industrial scale.
A further object is to make available a device for carrying out the method.
The object is achieved, according to the invention, in that a rotating press roller, a die and a piston are used for measuring the compression factor.
In accordance with the present invention, a method of determining a compression factor of powders for processing by a roller presses having roller diameters of 100 to 400 mm is proposed, which comprises the steps of filling a groove of a die with powder, introducing a piston into the groove, pushing the die on a rotating press roller until it touches a roller surface, opening an end of the die located opposite to the press roller and pushing the die downward on the press roller until the powder rests on the roller surface, during a measurement exerting a force on the piston for compressing the powder, and using a position of the piston in relation to the roller for measuring a compression factor.
The advantage of the method according to the invention is that, by means of a single press roller, in combination with a die for very small powder quantities, it is possible for the first time to have predetermination for dry granulation on roller presses of all types. It makes it possible, with the least possible outlay in terms of material, to obtain the important data for a reliable prediction as regards the dry granulation method with roller presses and to keep the powder quantity required for a test as small as possible.
By the second roller being simulated, the quantity required was basically halved. Since the filling worm was dispensed with, a narrow press roller could be selected. So that the measurement can be carried out for all current roller presses of different designs, the device according to the invention has different measuring systems.
It proved particularly advantageous to compress a powder introduced in a groove in a nip predefined therein.
It is expedient to compress the powder introduced in the groove with a predefined force.
It is particularly advantageous for the groove to be formed in a displaceable die. As a result of this arrangement, a second press roller can be dispensed with.
It is expedient to move a piston provided in the groove via a guide part and a guide rod and to read off, from a rule and a pointer, a travel which represents a measured value.
The resulting press force is measured in the case of a permanently predefined roller nip.
The resulting roller nip is measured in the case of a permanently predefined press force.
In the device, the rotating press roller is assigned a groove in a displaceable die and a piston via a guide part and a guide rod, a rule and a pointer. The advantage of this is that only a single press roller is required, with the result that the device is very simple. This device is suitable for determining the compression factor of powders, irrespective of the origin of a roller press.
On roller presses, because the press rollers are arranged in pairs, the typical entering angle is active in each case on the left and on the right roller, but is required only once for assessment.
The unit of measurement for the highest press force exerted instantaneously on the powder is: kN/cm of linear roller width. This force is applied at a theoretical line transversely to the roller at the location where the two rollers are nearest. So that as little powder as possible is required, this method employs rollers with a width of 1 cm. Wider rollers may also be used for comparative measurements, such as, for example, for scale-up validation.
So that behavior can be tested in the case of different roller diameters, the abutment may be mounted in different positions, so that press roller diameters of 100 to 400 mm from the various manufacturers can be simulated.